Abstract (Summary) Colitis associated cancer (CAC) is the most deadly and devastating complication of inflammatory bowel disease (IBD). With no effective preventive or treatment strategy for CAC it is important to understand how IBD induces CAC. Cytokines are small protein mediators of inflammation that are instrumental for IBD development, and may also exhibit tumor-promoting properties. This project is focused on the role of Interleukin 23 (IL-23) in regulation of chronic inflammation and CAC tumorigenesis. During the last 8 years I worked on different aspects of cytokine biology and the role of cytokines in inflammation, autoimmunity and cancer. For a long time our lab has used a azoxymethane+DSS induced CAC mouse model to mimic CAC development in humans. Using this model, our lab has shown a mechanistic connection between the transcription factor NF-B and tumorigenesis. Having long-term interest in how cytokines promote cancer, I have searched for pro-inflammatory cytokines, whose expression is controlled by NF-B, which mediate effects of inflammation on CAC. Such cytokines are better targets for therapy in comparison with global inhibition of NF-B itself. My preliminary data suggests an important role for IL-23 in CAC. I hypothesize that IL-23 increases tumor multiplicity and growth by activating several pathways, which maintain chronic inflammation and pro-survival pathways in epithelial and malignant cells, and eventually enhance tumor formation and growth. To study the role of IL-23 in CAC I will use various gene modified mice and a mouse model of CAC. I will pursue 5 separate Aims (2 Aims during Mentored phase and 3 Aims during Independent phase of the award): Aim1. Evaluate the role of IL-23 in CAC development, growth and progression Aim2. Explore molecular mechanisms of IL-23 action in CAC Aim3. Examine the contribution of different IL-23 responsive cell types in CAC tumorigenesis Aim4. Examine the contribution of different IL-23 dependent pathways (IL-17 and IL-22) in CAC tumorigenesis Aim 5. Determine the role of IL-23 at different stages of CAC tumorigenesis and the consequences of its genetic or pharmacological blockade The long-term objective of this study is to dissect a cytokine network required for CAC tumorigenesis and to establish IL-23 as master regulator of intestinal inflammation and CAC tumord evelopment. If proven that IL-23 is instrumental for both IBD and cancer development, this cytokine would represent an attractive target for specific therapy or prevention of CAC and IBD.